It is desirable in many industries to measure the torque between two relatively rotatable components which have a torque resistance between them. One example is the soft drink beverage industry where bottle-type containers are closed off by screw-type caps. Such threaded caps can be of the type having fully threaded members which must be screwed on tight to seal the contents, and subsequently unscrewed by hand action to permit dispensing of the contents. More commonly today, such threaded caps are of the type having only vestigial threads requiring a twist-off rupturing action for removal of the cap. Both types of caps must be applied so as not to leak, but may not be so tight as to make it difficult for the consumer to remove the cap by hand action only. Consequently, the amount of torque required for either type of cap must be within predetermined limits. Similar constraints apply to screw-type caps for other consumer products such as toothpaste, shampoo, and lotions of various sorts.
In such industries, particularly the soft drink industry, which employ capped containers it is a common practice to measure, on a sampling basis and for quality control purposes, the required cap removal force in order to determine whether it is within a desired range. Many different types of torque measuring devices and systems have been employed for such purposes. These range from simple cap testers to relatively complex ones, all of them employing means for grasping or gripping the caps and containers, and means for rotating one relative to the other.
A problem exists with the grasping means especially employed in cap testing in that too much compression force may be placed on the cap so that it is damaged, or deformed, thereby resulting in faulty torque readings, or the inability to measure torque. This is particularly a concern where it is desired to measure the torque required to remove and/or secure smooth metal caps.
Various devices have previously been suggested to serve as grasping means for caps in torque measuring systems. In one such bottle cap remover/torque tester, as shown by U.S. Pat. No. 4,794,801, issued Jan. 3, 1989 to T. M. Andrews et. al., a chuck comprising a circular disk having a shallow concave, conical dish shape on one side is provided with radiating teeth. These teeth are formed out of hardened steel and are sharp, and the teeth positively engage the cap at its periphery. Such teeth bite into the softer material of the cap, typically plastic or aluminum. Although the purpose of the chuck is to avoid rotational slippage, such a chuck may chew-up the cap, and may indeed rupture it to give faulty readings.
In another cap torque tester, such as shown by U.S. Pat. No. 4,539,852, issued Sep. 10, 1985 to Jerome H. Feld, a metal coil spring is used as a chuck. The coil spring has an inner diameter which is somewhat less than the outer diameter of the cap. A torque arm is provided to enable opening and closing of the coils of the spring, so that it can be placed over the cap and then tightened around the periphery of the cap. Such steel spring may also deform the cap periphery as it continues to be tightened and torque is applied. False readings can be obtained because if the cap is deformed, resistance to a torque force applied to unscrew the deformed cap may be greater than to an undeformed cap. This coil spring chuck will thus not duplicate the torque force applied by the human hand.
Another type of chuck for removing caps in a torque tester is shown in U.S. Pat. No. 4,716,772 issued Jan. 5, 1988 to K. B. Bubech et. al., which employs a motor driven three-jaw gripping device to grip and rotate the cap. This is similar to collets used in machine tools. However, it is not fully satisfactory for performing torque measurements on metal caps, since these jaws may put too much radial compression on the metal caps. In a similar arrangement as shown in U.S. Pat. No. 3,866,463, issued Feb. 18, 1975 to David A. Smith et. al. the bottle is rotated but the cap is held stationary by a three jaw chuck, with the same unwanted possibility of applying excessive radial compression on the cap.
Cap-grasping jaws in torque testing machines have been provided with elastomer (e.g. polyurethane) lined inserts as shown in U.S. Pat. No. 4,696,144, issued Sep. 29, 1987 to Geza A. Bankuty et. al. Although less surface damage may result because of the presence of elastomer, the grasping force is still applied radially to the cap by positively driven jaws. Thus, excessive radial compression may still be placed on the cap, with the result that the cap may be deformed.
A still further form of cap grasping mechanism is shown in U.S. Pat. Nos. 4,811,850 and 4,907,700 issued Mar. 14, 1989 and Mar. 13, 1990, respectively, to Geza A. Bankuty et. al. The cap grasping chuck described therein comprises a series of vertically arranged fingers deployed to surround the cap. The individual fingers each have an elastomeric coating on their inner lower portions. The upper portions of the fingers are surrounded by a collet ring which acts as a cam, and such collet can be moved downwardly on conical surfaces on the upper part of the fingers in order to cause the fingers to be flexed inwardly at their lower ends into cap grasping engagement. This form of engagement of a cap is equivalent to a multi-jaw chuck, even though the fingers are flexed inwardly rather than positively driven inwardly. This arrangement suffers from the possibility of the cap being distorted, despite the fact that the fingers are lined with elastomer, because steel fingers are used to apply a compression load radially to the cap. Also, the mechanism is relatively complicated.